The present invention relates to acoustics and sound modifying means for muffling and filtering air, and more particularly to devices for muffling and filtering air exhausted from pneumatically-operated hand tools, equipment, machines, and the like.
Pneumatic hand tools are commonly used in industrial and residential settings. Various types of pneumatic hand tools are available, including ratchets, drills, wrenches, grinders, sanders, etc. Known hand tools typically include a handle having a hollow internal chamber. The chamber includes an air intake passage and an air exhaust passage. Each passage extends between a motor and an opening in the bottom surface of the handle. The portion of the intake passage located near its respective handle opening includes components adapted to connect to a standard air coupler or the like. The coupler is in communication with a pressured air supply source. The exhaust passage opens to the atmosphere. When exhaust air is vented from the hand tool, a considerable amount of noise and particulate debris is generated, potentially causing auditory and/or respiratory damage to the operator and others located nearby.
Although ear plugs and face masks are available to workers, they are often not used for a number of reasonsxe2x80x94most typically because they are not convenient. Numerous attempts have been made by hand tool manufacturers, therefore, to reduce the amount of noise and particles generated by the hand tool itself. These attempts include designing quieter and cleaner motors and designing hand tool components that suppress noise and trap waste prior to expulsion from the hand tool. For example, U.S. Pat. No. 5,418,339 describes a pneumatic hand tool having an exhaust port filled with a web of non-woven fibers coated with a binder resin. These types of mufflers have had some success in muffling sound, but there is often an increase in back pressure to the motor causing a decrease in the operating efficiency of the hand tool. The operating efficiency of a tool is typically measured in the operating speed of the motor in revolutions per minute (rpm) at a certain gauge pressure.
Cylindrical canister-type combination muffler and air filters are known for large machines, such as hoists and presses. For example, U.S. Pat. No. 4,134,472 describes a combination muffler and air filter having a central tubular member with a number of slots. The tubular member is surrounded by a disposable canister having inner and outer perforated rigid cylinders encasing a series of stacked annular filter members. Exhaust air passes through the inner cylinder, into the filters, and out the outer cylinder. These devices are not typically used for hand tools, however, because of they are large, heavy, and difficult to maneuver.
Thus, there exists a need for a noise muffling system that can reduce sound levels and remove entrained solid and liquid contaminates from the exhausted air before it is discharged to the atmosphere. The ideal device would effectively muffle and filter the exhaust air without creating substantial amounts of back pressure. This would allow a hand tool to be operated without jeopardizing performance of the pneumatic tool over long periods of usage. The ideal muffling system would further attach to a hand tool body and remain attached even during significant tool vibrations. In addition, it would be desirable to have a muffler that can be easily attached to existing pneumatic hand tools. The present invention is directed to fulfilling these needs and others as described below.
In accordance with aspects of the present invention, a muffler is provided for use in a pneumatic hand tool having a handle with an exhaust passage. The muffler includes an inner tube, an outer tube, an upper plate, and end cap. The inner tube is located within the outer tube, with one or more openings being provided in each. The combination of inner tube and outer tube is located within the exhaust passage main section. The upper plate is located near the inner tube proximal end and is provided to close off the exhaust passage so that a majority of the exhaust air is directed into the inner tube during use. The end cap attaches to the handle for closing off the exhaust passage, but for one or more exit openings. During use, exhaust air enters the inner tube, flows out its openings, flows out the outer tube openings, and flows out the exit opening in the end cap. The tortuous path slows the exhaust air and assists in dampening exhaust noise. Various alternative embodiments are provided.